11.1.1. Function Templates

11.1.1. Function Templates
	11.1. Generics and Templates

[ fromfile: templates.xml id: functiontemplates ]

Function templates create type-checked functions that all work on the same pattern.

Example 11.1. src/templates/template-demo.cpp

[ . . . . ]

template <class T> T power (T a, int exp) {
  T ans = a;
  while (--exp > 0) {
    ans *= a;
  }
  return (ans);
}

The compiler will generate a function body for each different combination of calling types used in the client source code.

Example 11.2. src/templates/template-demo.cpp

[ . . . . ]


int main() {
  Complex z(3,4), z1;
  Fraction f(5,6), f1;
  int n(19);
  z1 = power(z,3);              
  f1 = power(f,4);              
  z1 = power<Complex>(n, 4);    
  z1 = power(n,5);              

}

	First instantiation: T is Complex.
	Second instantiation: T is Fraction.
	Supply an explicit template parameter if the actual argument is not "specific" enough. This results in a call to a function that was already instantiated.
	Which version gets called?

Each time the compiler sees a template function used for the first time with a specific combination of parameter types, we say the template is instantiated.
Subsequent uses of of power(Complex, int) or power(Fraction, int) translate into ordinary function calls.

	Note
	One important difference between overloaded functions and multiple specializations of the same template function is that overloaded functions must return the same type. Example 11.2 shows different versions of the template `power()` function with different return types. Overloaded functions must all have the same return type.


11.1. Generics and Templates		11.1.1.1. Exercises: Function Templates